v167 - cancel pending delayed frame on exit
Base: v166.
Hardware result for v166:
- star-page switching smooth
- no flash
- ORHACK main-menu entry still striped/slow

Targeted change:
on visual-page deactivation, send 'stop' to delay 125.
This cancels a pending B frame before ORHACK menu takeover.
The v166 active-page spigot remains as a second guard.

Shimmer timing unchanged:
one 250ms metro, A immediate, B +125ms.
Audio/AUX/LED untouched.
